1. Field of the Invention
The present invention relates to a method of fabricating a thin film transistor using a metal induced lateral crystallization (MILC) method, and more particularly, to a method of forming wires of a poly-crystalline thin film transistor by adding etch-stopper layer patterns when the poly-crystalline thin film transistor is fabricated using a MILC method, in which a silicon thin film of a semiconductor layer can be protected at the time of etching an interlayer insulation film for forming contact holes.
2. Description of the Related Art
In a method of forming a poly-crystalline silicon film which is used as a semiconductor layer of a thin film transistor, an amorphous silicon film is deposited on a substrate, and then processed at a predetermined temperature, to thus crystallize the amorphous silicon film into a poly-crystalline silicon film. Here, a metal induced lateral crystallization (MILC) method, a solid phase crystallization (SPC) method, and an eximer laser annealing (ELA) method are known as the amorphous silicon film crystallization method.
Among them, the MILC method does not only enable a batch processing using a conventional inexpensive heat treatment facility but also has many advantages of a relatively low processing temperature and a relatively short processing time.
A conventional method of fabricating a thin film transistor using a MILC method will follow with reference to FIGS. 1A through 1E.
FIGS. 1A through 1E are cross-sectional views for explaining a conventional thin film transistor fabrication method using a MILC technology, respectively.
Referring to FIG. 1A, an amorphous silicon film is deposited on an insulation substrate 10, and the amorphous silicon film is patterned using a semiconductor layer forming mask (not shown), to thereby form a semiconductor layer 11. Then, a gate oxide film and a gate electrode material are sequentially deposited on the entire surface of the substrate 10, and then sequentially patterned using a gate forming mask (not shown) to thereby form a gate electrode 13 and a gate insulation film 12.
Referring to FIG. 1B, high-concentration impurities are ion-injected on the substrate to form a source region 11S and a drain region 11D.
Referring to FIG. 1C, a photosensitive film is formed on the whole surface of the substrate, and then a photosensitive film pattern 14 which is slightly larger than the gate electrode 13 is formed. Then, a crystallization induced metal film 15 for metal induced lateral crystallization (MILC) (hereinafter referred to as a “MILC metal film”) such as nickle (Ni) is deposited on the entire surface of the substrate, to thereby form a Ni silicide in the amorphous silicon film of the semiconductor layer 11.
Referring to FIG. 1D, the photosensitive film pattern 14 is removed by using a lift-off method, to thus remove part of the Ni MILC metal film 15, and thus the gate electrode 13 and the part of the semiconductor layer 11 are exposed. Then, a heat treatment is performed for crystallizing the amorphous silicon film into a poly-crystalline silicon film.
Referring to FIG. 1E, an interlayer insulation film 16 is deposited on the substrate 10. Then, the interlayer insulation film 16 is patterned using a contact forming mask (not shown) to thus form contact holes 17.
In general, amorphous silicon or crystallized poly-crystalline silicon is not etched by a solution of fluoric acid (HF) which is an etching solution of a silicon oxide film which is used as an insulation layer of an interlayer insulation film. However, if nickle (Ni) is deposited on a semiconductor layer for MILC and then a crystallization heat treatment process is undergone as described above, a metal such as nickle (Ni) is added onto the semiconductor layer made of a silicon film. Accordingly, the nickle-added semiconductor layer is etched by a fluoric acid solution at the time of forming contact holes.
Thus, when a poly-crystalline silicon thin film transistor is fabricated using a conventional MILC method as described above, an interlayer insulation film is formed and then contact holes are formed by a wet etching process, In this case, since a Ni-included silicon thin film located below the contact holes as well as an insulation film is etched by a fluoric acid solution, it is difficult to form a transistor. In particular, since a thickness of a silicon thin film of a thin film transistor is 500 Å or less, at a trend of using an extremely thin film, the etching problem becomes further severe.
Thus, in order to prevent the above-described conventional etching problem, a fluoric acid etching process is carefully executed or a concentration of the fluoric acid is adjusted, to thereby optimize an etching speed. Otherwise, a dry etching process is used. However, these processes are very complicated so as to require for much processing time. Also, electrical features of transistors are not consistent, to thus cause a decisive factor of lowering a yield to occur.
According to another conventional technology to prevent the conventional defective phenomenon, nickle (Ni) is deposited after etching contact holes. In this case, a distance to be crystallized by the MILC method, that is, a distance between a contact hole and a gate electrode is too long and thus unrealistic. In particular, a crystallization speed is too slow to be industrially applied in the case of an N-TFT (N-type Thin Film Transistor).